Julian date 2459487, ten a.m., the Monday meeting.
At agenda item three, Zhou Yan put three histograms on the screen. Eight people in the room, half of them on their phones. She said: three baselines, same night, same shape; I want to check the instruments first. The people on their phones put them down.
She talked fast, five minutes: three plots, one timestamp, and one sentence—"I want to go in order, starting with the receivers." No one interrupted. People at this station were used to Zhou Yan not looking at anyone when she spoke; her eyes stayed on the plot, and plots are more persuasive than people.
Old Tang, the chief engineer, was the only one on the technical side senior to her. Old Tang looked at the plots, and his first reaction was not to the plots but to the date. "Last Monday?" he said. "There was a thunderstorm over at Miyun last Monday night. Their data is due for a discount to begin with."
"I cut the lightning-arrester intervals out of the Miyun data," Zhou Yan said. "The remaining sample is still seventy percent."
"The Kashgar and Miyun receivers came from the same procurement batch," Old Tang leaned back. "Did you check crosstalk?"
"Checked. Feed-line isolation is forty-seven decibels. Crosstalk can lift the noise floor; it can't grow a shoulder."
Old Tang neither agreed nor disagreed. Thirty years of managing equipment had taught him to hate reading an instrument's illness as the sky's, and to fear even more repairing the sky's illness into the instrument's—the first cost him face, the second cost him money. He rapped the table. "Let's be clear up front. If this ends up traced to the sky, I won't sign a single word of the equipment-replacement budget; if it ends up traced to my equipment, I'll sign, and retire on the spot." Somebody laughed. Zhou Yan didn't. She could hear it: eight parts of that joke were budget, two parts retirement.
The room went quiet for a few seconds. Engineer Hong from the equipment section raised his hand slowly. "If you ask me, check the feed first," he said. "That No. 7 feed of ours is an old thing. What filth hasn't it picked up?"
Zhou Yan didn't take it up. On the whiteboard she wrote an exclusion list: line one, "receivers"; line two, "clocks"; line three, "feed/antenna." She clicked the cap back on her pen and said: In order, one funeral at a time.
The phrase came out off the cuff. It would circulate in the field for years, and everyone would assume the first person to say it was dead.
With instrument hunts, the answer usually sits in the last place anyone wants touched. The No. 7 feed, antenna one, up the tower—Zhou Yan thought of it first, but she spent two days each on the receivers and the clocks before it—order is order; she wanted nothing anyone could fault. The atomic clock group cleared itself in two days: hydrogen-clock comparison records continuous, clock-offset prediction residuals at the picosecond level; a drift on the shoulder's scale could not be derived, could not be built, could not be faked. For the receivers she set a spare unit running in parallel; twenty-four hours later, on the new machine's baseline, the shoulder was still there.
On the fourth day she went up the tower, with Eli.
Eli was fifty-eight, thirty-one years at this station, skin the color of the gobi, palms all callus and old burns. He called the feed cabin the heart of the dish. He climbed without puffing; Zhou Yan puffed. She stopped to rest at rung two hundred seventy; Eli waited above her and did not hurry her.
The No. 7 feed sat in the northeast corner of the cabin, horn pointing down, and at its connector the stain soaked into the metal's grain was still there. Zhou Yan looked inside with the borescope, took a swab sample, and sent it down to the lab for assay. Crouching in front of the feed she asked, "When was this thing last serviced?"
"Serviced?" Eli turned the word into a question. He crouched down and wiped the nameplate with his sleeve; the lettering on it was worn down to half. "This heart of the dish, it looked like this when I came. Thirty years. Never been clean."
"Oil seepage affects the standing-wave ratio."
"It affects it," Eli nodded, very readily. "Always has. Pull your standing-wave record from six years ago and the one from now, put them together—the difference, that fraction of a decimal, can't be bothered to move." He stood up, his knee gave one crack. "If you ask me, that residual business of yours has nothing to do with the heart of the dish. The heart of the dish has an old illness. Old illnesses don't grow new symptoms."
That made no sense, but it was a long time before Zhou Yan worked out why it made no sense—because it sounded too much like a judgment and not enough like an inference. Eli had known this heart of the dish for thirty-one years, the way you know an old horse. The horse doesn't kick today, so Eli knows it didn't kick yesterday. Instruments don't know instruments; people know instruments. She never quoted the line in any report, but in her head she entered a merit for Eli.
She requisitioned thirty years of observation archives for the No. 7 feed.
The trouble sat at the other end. Before 2010, Kashgar's raw voltage records didn't go to disk; they went to tape. The tape library was under the main machine room, cardboard boxes, labels handwritten in ballpoint, blue ink, some of it already feathered. She filed for access; the archive office said the tapes had been catalog-scanned once, the scans existed, no need to touch the originals. She said she wanted the original sampling rate; the scans were frame-skimmed. The archive office said one of the two tape drives had died; the last one was in Ürümqi, and there was a queue.
She didn't idle through the queue. She asked for the instrument inventories of the other stations, and tabulated what feed Miyun and Nanshan each used—what model, which factory batch. Their feeds were not from the Kashgar procurement batch. The inventory arrived Friday afternoon. She was eating polu in the canteen, sitting by the window with the table spread out; when she picked up her chopsticks a drop of oil fell on the paper, square on the "feed model" column. She blotted it with a tissue and made it worse. In the end she went back to the machine room and retyped the whole thing from memory.
Unambiguous: three stations, three kinds of feed, two factory batches. One and the same shoulder. She built a noise template for each of the three feeds and matched them against the shoulder's spectral shape—an illness of the feed leaves the fingerprint of the feed, standing waves put periodic teeth in the spectrum. Three templates went on, three sets of teeth missed. The shoulder had no fingerprints. She saved the overlay into that cache-lookalike directory of hers, dithered a long while over the filename, and finally just called it "3t." She didn't know whom she was guarding against.
She ate half that plate of polu. Not for lack of appetite—she forgot to eat.
The tape drive came round to her on Thursday of the following week. The Ürümqi machine came over with it, plus an operator ten years younger than her, who asked first thing at the door for a grounded power strip. The tapes went through one by one; one snagged, and the operator pried at the tape base with a pencil for twenty minutes. Zhou Yan stood by watching. It was cold down in the machine-room basement and she was dressed thin; her right hand stayed in her pocket.
The operator's name was Ma, and while he pried he lectured: metal tape like this, gamma ferric oxide for the magnetic coating—kept well, the signal holds fifty years; kept badly, it starts dropping at thirty. She said these tapes had always lived in cardboard boxes. Xiao Ma said you're lucky, then—gobi air is dry; put them at some humid station in the south and they'd have turned to brick long ago. She said mm. What she was thinking of was not the magnetic coating but the duty operator who thirty years ago had sat at this machine: he finished taking this tape, signed the duty sheet, locked up, went home, and went his whole life without knowing what he had recorded.
The tape was from March 2004. Her pick was not random: in March that year, solar activity sat at its minimum—the ionosphere at its quietest, man-made RF at its least; the cleanest month in thirty years. If the shoulder had been there thirty years ago, the cleanest month was where it would show.
Digital-to-analog conversion, sampling, onto disk. From the first hour of data she made a residual line. The program finished at 5:40 in the afternoon; outside the machine-room window the sky was still light. The plot came up and she enlarged it.
At the right shoulder, a spike.
Not a shoulder—a spike, far narrower, like a shoulder that hadn't finished growing. Significance 2.6 sigma; on its own, nothing, the kind you cross out over a sip of tea. But she wasn't looking at it on its own. She stacked it on last Monday's shoulder: the position matched. The width—the one thirty years ago narrow, today's wide—had spread sixfold. She pulled the No. 7 feed's thirty-year standing-wave records and drew a trend line: flat, sagging slightly, aged by zero point two over thirty years. An instrument's aging is a straight line; the spike's broadening is a curve rising. The two lines crossed once on her plot, the crossing sitting around 2012—from then on, the instrument's illness was heading down and that thing was heading up.
She sat there without moving. The operator was putting the tapes away, boxing them one by one, gently, like collecting someone else's letters.
A thing was getting wider. Getting wider meant it was not an instrument's illness—an instrument's illness breaks, rusts, cuts out; it does not grow. In her notebook she wrote: Illness does not grow. When she finished she stared at the words herself, and felt her hair move. Not fear; she could tell fear apart. It was something stranger: an instrument had gone wrong, she had fixed instruments half her life, and this was the first time she felt like the one who didn't know the rules.
She called Eli. He was home at dinner; a TV could be heard behind him. She said: Master Eli, the No. 7 feed, March 19 to 26, 2004—does that ring any bell, did it act up around then?
The chewing on the other end stopped. "March of '04," Eli said. "I was in training in Ürümqi that month. Can't remember who I left the heart of the dish with. What, did you find a fault?"
"Not yet," she said. "You'll know when I do."
"You," Eli said, "hunt a thing the way other people hide a thing."
She hung up and stood in front of the machine-room window. Full dark outside; antenna two was turning, tracking a star that had passed overhead at dusk, and from her angle the lock indicator was a very low red star, brighter than anything in the sky.
Friday evening she went to Eli's workshop. It sat at the far end of the logistics yard: an old bench vise, one wall of tools, thirty years of duty sheets nailed to the wall. Eli poured her tea, brick tea, salted. She asked about the origins of the No. 7 feed. Eli said there weren't any, really—experimental units from the nineties, split among three stations; Kashgar got the tail of the lot. The acceptance report said, "residual defect from surface-treatment process, no effect on electrical performance." Eli said: even back then I thought—no effect on electrical performance, so it affects something else. I asked, affects what? The acceptance man said: your mood.
She said: so it stayed dirty all this time, and none of you ever did anything?
Eli said: it's not that nothing was done. The '98 overhaul—money came down from above, a new feed went in, lasted one month, and the data people came running to say the new feed's noise floor was a few tenths higher than the old one's, clamoring to swap back. So it was swapped back. Guess why. Zhou Yan shook her head. Eli drank a mouthful of tea: because the old one—thirty years of it—had all its temper in the records. The new one was clean, and a clean thing has no history. If your residuals have to be compared with the '98 residuals, you use this heart of the dish. It's dirty. It's dirty evenly.
She walked back to the dormitory that night; the wind was hard. Dirty evenly—she turned the words over once in her head. A systematic error that has held still for thirty years can serve as a baseline. And suddenly she understood what she really had to thank this heart of the dish for: precisely because its old illness was on the record, the new spike could not be it. Old illnesses don't grow new symptoms. When Eli said that, he didn't know he was doing physics.
The next day she sent out three letters, with the tape's spike plot attached. One to Miyun, one to Nanshan, one to Shanghai Observatory—Shanghai kept a tape library sealed even longer. On the letterhead she wrote "instrument-fault investigation, request for assistance," wording aimed at the instruments. She wasn't ready to let anyone think elsewhere yet. Not to keep it to herself—or so she told herself; it was controlling variables: let everyone walk the instrument leg to its end first; walked dead, whatever remains can stand. Until that leg was finished, she would not say one word more.
Three days later, two replies arrived. Miyun's said they had swapped in a spare of the same feed model, re-observed, residuals clean. Nanshan's was blunter: their feed differed from Kashgar's in model, and the contemporaneous residuals in their archives had been clean to begin with.
Zhou Yan laid the two replies side by side on the desk and looked for a long time.
Clean. Other stations, other feeds, other decades—clean. Only Kashgar, only No. 7, a spike not yet grown thirty years ago, and now, in her hands, grown into a shoulder.
By the order of the exclusion list, the instrument item had had its funeral. The meaning of the funeral was: at the end of the hunt, what got buried was not the instrument but the last road she could understand. She picked up the pen and drew a line through "feed/antenna" on the whiteboard. The line came slowly, and straight.
When it was done she found herself thinking about something entirely unrelated: Eli said the heart of the dish hadn't been clean in thirty years. Thirty years unclean—and that layer of stain soaked into the metal's grain, what was it? She flipped back to the swab assay report: oil, dust, and a trace of organic residue the report tagged "origin unknown."
She closed the report and looked at the wall clock. Twenty-three seventeen. She picked up the paper notebook, started a new line under "Illness does not grow," and this time wrote a date: 2004, 3, 19.
The pen ran dry. She shook it, and took another.